The subject of the present invention is the production of a mounting rim for a tire which can form, with a tread support ring and said tire, a rolling assembly which can be used in the event of travel where the inflation pressure drops abnormally relative to the nominal use pressure, referred to as the operating pressure, the inflation pressure possibly even being canceled out.
This invention relates more particularly to the connection of a support ring to a rim onto which said ring has been slipped.
In the case of a mounting rim comprising two rim edges, two seats of respective diameters "PHgr"1 and "PHgr"2 and, located between the two seats, a bearing surface having an essentially cylindrical shape of minimum development Dp at least equal to the development of any rim part located axially between the axially inner end of a rim seat and the rim edge axially closest to said rim seat (see the example shown in FIG. 1), it is possible to effect the mounting of a support ring by slipping the latter around said rim seat in order to bring it, by sliding, onto the bearing surface as far as the desired position.
For this type of rim and ring assembly, there is a need to have a ring which remains integral with the rim without causing an imbalance of the unbalanced-mass type when this assembly is caused to rotate, while permitting easy mounting of the ring on its bearing surface.
Furthermore, and taking into account the irregularities in production of the rims, in particular of sheet metal rims, it is necessary to be able to achieve mounting of the support ring which is fairly lacking in sensitivity to these irregularities in order to have a ring and rim assembly which is as balanced as possible.
To this end, and in accordance with the present invention, there is proposed a rim, intended for mounting a tire comprising at least two beads, which rim is defined axially by a first rim edge and a second rim edge, comprising, viewed in meridian section, at least a first rim seat axially adjacent the first rim edge and a second rim seat axially adjacent the second rim edge, at least the first rim seat having a generatrix, the axially inner end of which is on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, and at least one bearing surface intended to receive an annular bearing support, said bearing surface being arranged between the axially inner ends of the first and second rim seats; this bearing surface being of total axial width Lp and having an essentially cylindrical shape of minimum development Dp at least equal to the development of any rim part located axially between the axially inner end of the first rim seat and the first rim edge.
The rim according to the invention is characterized in that the bearing surface comprises at least one surface clamping part, each surface clamping part being regularly distributed in the circumferential direction over said bearing surface and having a maximum external development Ds, measured on an enveloping surface concentric to the bearing surface, which is strictly greater than Dp, in order to create mechanical clamping when the support ring is mounted, between said ring and said surface clamping part, which is appropriate to ensure holding of said ring on the bearing surface and, inter alia, to limit or even prevent any relative displacement in the circumferential direction between the ring and the rim.
A surface clamping part is defined as a continuous or discontinuous additional thickness over the bearing surface which is intended to create clamping forces between the support ring and said bearing surface, this additional thickness being arranged substantially along a circular line perpendicular to the axis of rotation of the rim.
xe2x80x9cRegularly distributed in the circumferential direction over the bearing surface of the rimxe2x80x9d is understood to mean a surface clamping part which forms a relief protrusion on said bearing surface and which is:
either continuous in the circumferential direction around the bearing surface;
or composed of a plurality of elements in relief, the circumferential distances between each of said elements being substantially equal; these elements in relief are arranged along a circular line concentric to the bearing surface.
xe2x80x9cEnveloping surfacexe2x80x9d is understood to mean the cylindrical surface of lesser development which envelops a surface clamping part. When this enveloping surface has as its axis of symmetry the axis of rotation of the rim, this means that the enveloped surface clamping part has the same radial offset relative to the bearing surface of development Dp.
xe2x80x9cDevelopmentxe2x80x9d is understood to mean the circumferential length or extent of an actual or virtual cylindrical surface.
When use is made of a support ring, the minimum development of the internal surface of which is substantially equal to the development Dp of the bearing surface, a degree of clamping, referred to as Ts, can be defined on each surface clamping part which is equal to the ratio (Ds-Dp)/Dp. Judiciously, the value of the development Ds of each surface clamping part is selected such that this degree of clamping Ts enables the support ring to be put in place on the rim while maintaining sufficient clamping to prevent sliding of the ring relative to the rim when the rim and support ring assembly is driven in rotation.
For a given degree of clamping between a support ring and a surface clamping part, it is preferable for the axial width Ls of said part to be between 10% and 50% of the axial width Lp of the bearing surface in order to limit the effort to be provided for putting the ring in place on this surface clamping part. When the axial width Ls of a surface clamping part is less than 10% of the axial width Lp of the bearing surface, the clamping forces are not sufficient to ensure good holding of the support ring on the rim; when the axial width Ls of a surface clamping part is greater than 70% of the axial width Lp of the bearing surface, the efforts to be provided for effecting mounting of the ring become excessive and may either prevent mounting or induce within the support ring excessive stresses which are harmful to good fatigue strength over time.
Provision may be made to provide on the bearing surface of a rim a plurality of surface clamping parts which are distributed in the axial direction over the bearing surface, each surface clamping part having a specific development and width which may be identical or alternatively different. Preferably, and for a degree of clamping selected for each surface clamping part, the total of the widths of said surface clamping parts will be between 15% and 70% of the width Lp of the bearing surface. These values are intended to ensure easy mounting and satisfactory clamping of a support ring on the rim.
With the aim of facilitating the putting in place of the support ring on the rim, each surface clamping part may be connected to the bearing surface, on the side of the rim seat from which the support ring is slipped on, by means of a surface generated by a generatrix which is connected at a first point to the surface clamping part and at a second point of the bearing surface, the straight line passing through said two points forming an angle other than 90xc2x0 with the axis of rotation of the rim. This same characteristic may be provided on both sides of each surface clamping part in order also to facilitate the demounting of the support ring.
Another variant embodiment consists in forming on a rim and on the part thereof axially farthest from the rim seat onto which the support is slipped, a surface clamping part of frustoconical shape which merges with the axis of rotation, and the generatrix of which forms with the axial direction an average angle of between 1xc2x0 and 5xc2x0, the minimum development of said surface part being on the side of the rim seat onto which the support is slipped.